It is known from U.S. Pat. Nos. 2,459,128 and 2,389,217 that malononitrile is produced by preparing cyanoacetamide from monochloroacetic acid and sodium cyanide and, then, by converting cyanoacetamide to malononitrile by means of dehydration.
In this process, sodium cyanide, which is virulently poisonous and, therefore, should be extremely carefully handled, is used. Also, the process is composed of a plurality of steps. Furthermore, in the step of dehydrating cyanoacetamide, it is necessary to use an expensive additional material. Therefore, the above-mentioned process is unsatisfactory from the point of view of industrial utility.
Also, it is known from U.S. Pat. Nos. 2,553,406 and 2,606,917 and British Pat. No. 1,228,540 that malononitrile is prepared by reacting acetonitrile with cyanogen chloride at an elevated temperature of from 800.degree. to 1000.degree. C. This process is disadvantageous in the following ways. That is, since the reaction for producing malononitrile is carried out at a high temperature of from 800.degree. to 1000.degree. C., the reaction should be effected in a specific heat-resistant apparatus, which is expensive. Also, the high temperature reaction causes the reaction product to be contaminated with by-products, for example, carbon and polymers. Furthermore, the reaction product contains maleonitrile and fumaronitrile, which have boiling points close to that of malononitrile. Therefore, it is difficult to separate and purify malononitrile from maleonitrile and fumaronitrile by a usual separating and purifying method.
Furthermore, Japanese patent application publication (Kokoku) No. 47-28968 (1972) discloses a process for producing malononitrile by the catalystic ammonoxidation of .beta.-aminopropionitrile in the presense of ammonia and a catalyst. However, this process is disadvantageous in the following ways. That is, the yield of malononitrile is unsatisfactorily poor. The ammonoxidation reaction can be effected only in the presence of a large amount of ammonia. Accordingly, in the process, not only a large amount of ammonia is consumed, but also, a large amount of a neutralizing agent is used for neutralizing the reaction mixture. This feature makes it necessary to apply a complicated treatment to the waste water from the process and the cost of the process becomes undesirably high. Furthermore, when the resultant malononitrile is separated and recovered from the reaction mixture containing a large amount of ammonia, it is unavoidable that a portion of the resultant malononitrile becomes lost, because an alkaline substance added into an aqueous solution of malononitrile causes malononitrile to be remarkably chemically unstable and to be polymerized in the alkaline aqueous solution. Moreover, the large amount of ammonia in the reaction mixture causes the catalytic activity of the catalyst to decrease with the lapse of the reaction time.